Constant velocity universal joints to be used as, for example, means for transmitting a rotational force from an engine of an automobile to wheels at constant velocity are classified into such two types as a fixed type constant velocity universal joint and a plunging type constant velocity universal joint. The two types of constant velocity universal joints have a structure capable of transmitting rotational torque at constant velocity even when two shafts, namely, a drive shaft and a driven shaft are coupled to each other to form an operating angle.
As a constant velocity universal joint, for example, which is assembled to a propeller shaft used in automobiles, such as a 4-wheel drive (4WD) vehicle and a rear-wheel drive (FR) vehicle, there is known a plunging type constant velocity universal joint disclosed in Patent Literature 1.
In the constant velocity universal joint of this type, a lubricant such as grease is sealed in an inside of the joint, and thus a lubricating property is ensured in sliding regions in an inside of the joint when the joint is operated to rotate while forming an operating angle. Accordingly, in order to prevent a leakage of the lubricant sealed in the inside of the joint, the constant velocity universal joint has a structure in which a large diameter end portion of a boot is fitted onto one open end portion of an outer joint member, and a small diameter end portion of the boot is fastened and fixed by a boot band onto a shaft extending from an inner joint member.
The boot fitted onto the constant velocity universal joint disclosed in Patent Literature 1 has a structure in which, in addition to a portion fastened and fixed by the boot band, a lip portion abutting on an outer peripheral surface of the shaft is provided on an inner peripheral surface of the small diameter end portion. In this manner, the lip portion exerting a sealing function is provided, and thus a sealing property exerted by the boot is increased, thereby attaining secure prevention of the leakage of the lubricant sealed in the inside of the joint.